This invention relates to trolley wheels and, more particularly, to an improved trolley wheel which has a higher load bearing capacity and is longer wearing and more durable, as well as to a method for making the improved trolley wheel which avoids previous manufacturing difficulties and expense.
Trolley wheels have long been used in many industries, especially in overhead and other conveyors. Such wheels typically support suspended brackets which transport goods through various processes. For many years, metal trolley wheels were used and were subject to wear, corrosion, deterioration and were also noisy in operation.
More recently, combination metal and plastic trolley wheel assemblies have been devised which have greatly advanced the industry because of their many advantages. One such trolley wheel is that disclosed in copending, commonly assigned United States patent application Ser. No. 528,794, filed Dec. 2, 1974, entitled SANITARY ANTIFRICTION TROLLEY WHEEL invented by Frederick R. Sytsma. This trolley wheel essentially utilizes a pair of metallic outer bearing race rings fitted adjacent a central opening in an antifriction plastic trolley wheel with an inner race assembly extending through the opening and a pair of full complement rows of antifriction ball bearings between the inner and outer races. The outer race rings were spaced apart in a predetermined spacing by a portion of the plastic wheel.
A difficulty which has been encountered with such prior wheels is that the portion of the wheel which spaced the outer race rings apart is critical to the spacing of the bearings and thus the proper functioning of the trolley wheel assembly. Because of material shrinkage during manufacture of the wheels, it was difficult to obtain the critical dimensioning necessary for the wheel, and especially the portion intermediate the outer races, prior to insertion of the outer race rings therein.
Another difficulty encountered during use was that of the rotation of the outer metallic bearing race rings with respect to the antifriction plastic wheel. Such rings were also difficult to maintain in axial alignment with the wheel. Rotation of the rings with respect to the wheel causes heat buildup and wear reducing the life of the wheel. Excessive wear throws the bearings out of alignement.
Also, prior outer race ring configurations have required drawing of a portion of the rings meaning that the material used had to be sufficiently ductile to allow that drawing. Incorporation of sufficient ductility in the metallic material prevented the use of harder, longer-wearing materials and limited the load capabilities of the assembly.
Therefore, a need has existed for an improved trolley wheel assembly which maintains the advantages of the more recently designed metal-plastic trolley wheel assemblies useful in sanitary, overhead conveyor applications and yet overcomes the above-mentioned problems of manufacture, maintenance, and use.